Butter a
9X13 pan.Preheat oven to 350.In a bowl whisk together the flour, the
baking powder, and a pinch of salt and in another bowl stir together the sour
cream and the baking soda.

In a large
bowl cream together the butter and 1 cup of the granulated sugar until the
mixture is light and fluffy, add the eggs, 1 at a time, beating well after each
addition, and beat in the vanilla and lemon zest. Stir in the flour mixture
alternately with the sour cream mixture and stir the batter until it is
combined well.Pour the batter into a
buttered 9 X 13 cake pan. Sprinkle blackberries evenly on top.

In a small
bowl stir together melted butter, flour and sugar until it is sort of dough
like and stuck together.Crumble topping
mixture all over cake

Bake the
cake in the middle of a preheated 350°F. oven for 35 to 45 minutes, or until a
tester comes out clean. Transfer it to a rack, and let it cool.Serve warm or room temperature.(This is best the day of baking.)